nerdexam
GIAC

GSEC · Question #100

What is the function of the TTL (Time to Live) field in IPv4 and the Hop Limit field in IPv6 In an IP Packet header?

The correct answer is A. These fields are decremented each time a packet is retransmitted to minimize the possibility of. TTL in IPv4 and Hop Limit in IPv6 are decremented at each router hop and cause packet discard at zero to prevent infinite routing loops.

Networking and Core Concepts

Question

What is the function of the TTL (Time to Live) field in IPv4 and the Hop Limit field in IPv6 In an IP Packet header?

Options

  • AThese fields are decremented each time a packet is retransmitted to minimize the possibility of
  • BThese fields are initialized to an initial value to prevent packet fragmentation and fragmentation
  • CThese fields are recalculated based on the required time for a packet to arrive at its destination.
  • DThese fields are incremented each time a packet is transmitted to indicate the number of routers

How the community answered

(20 responses)
  • A
    85% (17)
  • C
    10% (2)
  • D
    5% (1)

Why each option

TTL in IPv4 and Hop Limit in IPv6 are decremented at each router hop and cause packet discard at zero to prevent infinite routing loops.

AThese fields are decremented each time a packet is retransmitted to minimize the possibility ofCorrect

TTL and Hop Limit are set to an initial value by the sender and decremented by one at each router the packet traverses. When the value reaches zero, the router discards the packet and sends an ICMP Time Exceeded message to the source, preventing packets from circulating indefinitely due to routing loops.

BThese fields are initialized to an initial value to prevent packet fragmentation and fragmentation

TTL and Hop Limit have no role in preventing fragmentation; fragmentation is controlled by the MTU and the Don't Fragment bit in the IPv4 header or Path MTU Discovery in IPv6.

CThese fields are recalculated based on the required time for a packet to arrive at its destination.

TTL and Hop Limit are not recalculated based on estimated travel time to the destination; they are simple hop-count decrements applied by each router regardless of timing.

DThese fields are incremented each time a packet is transmitted to indicate the number of routers

These fields are decremented, not incremented; an incrementing router-count field describes the IP Record Route option, not the TTL or Hop Limit mechanism.

Concept tested: IPv4 TTL and IPv6 Hop Limit routing loop prevention

Source: https://www.rfc-editor.org/rfc/rfc791

Topics

#TTL#hop limit#IPv4#IPv6 packet header

Community Discussion

No community discussion yet for this question.

Sign up to join the discussion
Full GSEC Practice